Delirium in the post-operative setting is common and is associated with significant morbidity, mortality, and cost. Elderly patients are at a particulary high risk for postoperative delirium, and as the US population ages, more elderly patients will present for surgery. Long-term sequelae of postoperative delirium include increased mortality, decreased cognitive function, decreased functional outcomes, and increased hospital costs. Although many factors may contribute to post-operative delirium, inadequate intraoperative cerebral blood flow (CBF) may be an important modifiable cause. Elderly patients, with high rates of hypertension and cerebral vascular disease, may require higher than expected blood pressures to maintain adequate CBF. Currently, anesthesiologists maintain blood pressure above empiric targets, with the assumption that CBF is adequate. However, no routine clinical monitor is currently used to directly measure CBF, and so elderly patients are at high risk of cerebral hypoperfusion. Recently, novel technology has been developed to assess the adequacy of CBF in real time, in individual patients. By monitoring individual patients at high ris for postoperative delirium, a potential association could be identified between inadequate CBF and postoperative delirium. This observational study will enroll 100 patients greater than 70 years old undergoing spine surgery at Johns Hopkins Hospital. Each patient will undergo rigorous preoperative cognitive testing. Intraoperatively, the adequacy of CBF will be assessed in real time. Postoperatively, the incidence of delirium and long-term cognitive dysfunction will be evaluated. The specific aims of this project are: 1. To assess whether the duration of time during surgery that a patient's blood pressures is outside the limits of CBF autoregulation is associated with postoperative delirium. 2. To assess whether the development of postoperative delirium is associated with cognitive dysfunction 3 to 6 weeks after spine surgery. The long-term objectives of this project are to reduce the incidence of postoperative delirium through monitoring of CBF, to predict the development of postoperative delirium, and to prevent cognitive decline that may result from delirium. If successful, this project will identify an important risk factor for postoperative delirium, that could be modified intraoperatively.